This invention relates to an electrophotographic photosensitive member having a photosensitive layer comprising a combination of a carrier generating phase and a carrier transporting phase provided on an electroconductive support.
Up to date, it has been proposed to constitute the photosensitive layer of an electrophotographic photosensitive member by combining a carrier generating layer (hereinafter referred to as "CGL") comprising a carrier generating material (hereinafter referred to as "CGM") which generates charged carrier (hereinafter referred to merely as "carrier") with a carrier transporting layer (hereinafter referred to as "CTL") comprising a carrier transporting material (hereinafter referred to as "CTM") for transporting either one or both of the positive or negative carrier generated in the CGL. Thus, by imposing the two basic necessary functions of generation of carrier and its transportation on separate layers, the materials available for constitution of the photosensitive layer can be chosen from wider scope of materials, and also it is rendered possible to select materials or material systems capable of fulfilling optimally the respective functions independently. Also, by doing so, it is rendered possible to constitute an electrophotographic photosensitive member having various characteristics required in electrophotographic process, for example, excellent characteristics such as high surface potential when it is charged, great charge retentivity, high photosensitivity and great stability in repeated uses.
As the photosensitive layers of the prior art, for example, the following constitutions are known:
(1) Constitution wherein a CGL comprising amorphous selenium or cadmium sulfide and a CTL comprising poly-N-vinylcarbazole are laminated.
(2) Constitution wherein a CGL comprising amorphous selenium or cadmium sulfide and a CTL containing 2,4,7-trinitro-9-fluorenone are laminated.
(3) Constitution wherein a CGL comprising a perylene derivative and a CTL containing an oxadiazole derivative are laminated (see U.S. Pat. No. 3,871,882).
(4) Constitution wherein a CGL comprising Chlorodian Blue or Methyl Scarilium and a CTL containing a pyrazoline derivative are laminated (see Japanese Provisional Patent Publication No. 90827/1976).
(5) Constitution wherein a CGL comprising amorphous selenium or its alloy and a CTL containing a polyaryl alkane type aromatic amino compound are laminated (Japanese Provisional Patent Publication No. 80130/1979).
(6) Constitution wherein a CGL containing a perylene derivative and a CTL containing a polyaryl alkane type aromatic amino compound are laminated (Japanese Provisional Patent Publication No. 126036/1979).
Thus, a large number of this kind of photosensitive layer have been known, but the electrophotographic photosensitive member having such a photosensitive member has the drawback of a very short usage life due to excessive electrical fatigue of the photosensitive layer when provided for use repeatedly in electrophotographic process.
For example, when provided for use repeatedly in electrophotographic process, the history of the potential of said electrophotographic photosensitive member cannot be maintained stably to give no stable image forming characteristic.
Also, use of a specific bisazo compound as CGM is disclosed in, for example, Japanese Provisional Patent Publications No. 117151/1980 and No. 145142/1979. However, the above drawback is considerably great even in the combination of this CGM with the CTM which is stated to be combinable. As can be understood also from this fact, a carrier transporting material effective for a specific carrier generating material is not necessarily always effective for other carrier generating materials, or conversely a carrier generating material effective for a specific carrier transporting material cannot be stated to be always effective for other carrier transporting materials. When the combination of both materials is inadequate, not only the electrophotographic sensitivity is lowered, but the so called residual potential becomes large, particularly due to poor discharging efficiency during low electric field, and, in the worst case, potential is accumulated every time of repeated uses, whereby it can be no longer practically useful for electrophotography.
Thus, as to the preferable combination of a material for constituting a carrier generating phase and a material for constituting a carrier transporting phase, there is no general rule in choice thereof, but it is required to determine practically an advantageous combination from among a large number of groups of materials.
An object of the present invention is to provide an electrophotographic photosensitive member which is provided with a carrier generating phase and a carrier transporting phase, has a high sensitivity and can form constantly good visible images while maintaining the history of the potential even when provided for use repeatedly in electrophotographic process.